The present invention relates generally to packaging, and more particularly to composite paperboard and plastic packaging for both liquid and dry products, including food products. More specifically, the present invention is directed to a process improvement for combining paperboard and a blow molded polymer film to produce a composite package.
Composite paperboard and polymer packaging of this type is well known as disclosed for instance in U.S. Pat. Nos. 5,009,939; 5,169,470; and 5,122,399, all assigned to the present assignee herein. Such packages combine the structural strength and superior printable surfaces of paperboard as an outer shell, and the liquid impervious, sanitary and barrier properties of a blow molded polymer film as an inner liner. In the past, printed matter has been applied directly to blow molded containers, or to labels which were subsequently applied to the containers particularly as shown in U.S. Pat. No. 3,207,822, but experience has shown that the combination of an outer shell of paperboard and an inner liner of a blow molded polymer film provides a superior product.
Generally, such composite packages are prepared from C1S (coated one side) paperboard wherein the polymer film is adhered to the uncoated surface of the paperboard leaving the coated surface for printing. The polymer film may be prepared from a single material such as polyethylene, polypropylene, polyester, etc., or it may comprise a coextruded sandwich consisting of one or more layers of polymer, adhesive tie materials and other barrier materials. In any event, some blow molding polymers do not adhere well to paperboard. Where such difficulties are encountered, it has been found necessary to apply an adhesive to the uncoated surface of the paperboard to achieve a good bond with the polymer film. However, as disclosed herein, a process improvement has been discovered which can be practiced during the blow molding process to achieve a good bond between the polymer film and the paperboard without the use of adhesives or the like.